Method and apparatus for bending glass sheets



Jan. 18, 1966 H LEFLET, JR 3,230,062

METHOD AND APPARATUS FOR BENDING GLASS SHEETS Filed Sept. 25, 1961 IN V EN TOR.

A TTORN E YS United States Patent 3,230,662 METHOD AND APPARATUS FOR BENDING GLASS SHEETS Herbert A. Letlet, .Ira, Toledo, Ohio, assignor to Libhey-Gwens-Ford Glass Company Filed Sept. 25, 1961, Ser- No. 140,324 7 Claims. (Cl. 651tl3) This invention relates broadly to the bending of glass sheets and, more particularly, to a novel method and apparatus for simultaneously bending a plurality of glass sheets arranged in superimposed stacked relationship.

It has previously been recognized that the most efficient manner of manufacturing a bent glass laminate, for example, an automobile windshield or an aircraft canopy glazing, is to bend all of the sheets which are to form a given laminate at the same time so that the curvature of each of the sheets will be substantially identical. At the same time, however, a serious problem has been encountered when attempting to so bend a plurality of sheets simultaneously, namely, the occurrence of pit ting in the surfaces of the glass sheets which are disposed in contact with each other.

Heretofore, various solutions have been suggested for eliminating this pitting problem, which has generally been believed to be caused by the presence of dirt and the like on the surfaces of the sheets prior to their being stacked on the bend ng molds together with the entry of foreign matter, present in the atmosphere of a bending urnace, between the sheets during the bending operation. For example, extreme care has been taken in washing the sheets to be bent prior to their being positioned on the molds. In addition, it has been suggested to place a screening material in spaced, surrounding relationship to the molds during their passage through the bending furnace. However, while the practices previously employed have been beneficial, the losses or number of rejects in bending glass sheets for laminates have remained relatively high, this being especially true in cases where relatively sharp bends in certain portions of the sheet are necessary which require those portions to be heated to a relatively high temperature.

One feature which would appear to indicate that the objectionable marring may be caused at least in part by the entry of particles of some kind between the sheets during the bending operation is the tendency of the sheets to bow toward their outer major surfaces during the initial portion of the bending cycle thereby leaving an opening into which abrasive material and the like may be blown. In this respect, however, it has been found that the bowing only causes a gap or separation in the sheet edges themselves, of any significance, along those corresponding edges of the superimposed glass sheets which are unsupported during the initial portion of the bending cycle, or when the sheets are disposed in a substantially flat, unbent condition. This is believed due to the fact that when the sheets are heated to a temperature beyond their softening point, they start to sag into conformity with the whole shaping surface, whereby the sheets become nested and will of themselves prevent passage of foreign matter therebetween.

The fact that the marring or pitting problem has still remained somewhat acute even where the sheets were first thoroughly washed and other precautions taken to inhibit entry of foreign matter in the furnace atmosphere between the sheets has led to the belief that this pitting is not caused, for the most part, by such atmospheric dirt, and while the invention is in no way to be limited by any theory, it is believed that the majority of the pitting is in fact caused by the spalling of pieces of glass from the edges of the sheets during the initial portion 3,23%,bb2 Patented Jan. 18, 1%66 'ice of the heating cycle. Further, although such spalling would occur along the supported edges as well as along the unsupported ones, the bowing of the sheets along the supported edges is, as previously mentioned, not severe enough to permit entry of the spalled pieces to any significant extent.

In any respect, it'has been discovered, and the instant invention is based upon such discovery, that retarding the heating of the unsupported edges of the superimposed sheets during the initial period of the bending operation, together with shielding these edges during such period to prevent entry therein of foreign materials completely eliminates or at least greatly reduces the occurrence of pitting. In this connection, one rnethod or means which has been found to be especially effective in greatly reducing the pitting problem is the employment of a thin, flexible curtain or screen, e.g. of metal or glass cloth or other similar material, which may be carried by the bending apparatus and is positioned so as to extend or project downwardly over and in contact with the unsupported edges of the sheets during the initial heating period. It is believed that the provision of such a curtain, due to its relatively large surface area in comparison with the sheet edges, acts to absorb heat from the atmosphere during this initial period of heat application and thereby retards the heating of the edges and prevents any significant amount of spalling normally caused by the rapid heating thereof. In addition, the cur tain, being immediately adjacent the edges, effectively prevents any entry of foreign material from the furnace atmosphere into the space resulting from the bowing of the sheets.

It is, therefore, the principal object of the present invention to provide an improved method and apparatus for bending glass sheets.

More particularly, it is an object of the invention to provide an improved method and apparatus for simultaneously bending a plurality of glass sheets disposed in superimposed stacked relationship.

Another object of the invention is the provision of a novel method and apparatus for eliminating, or at least greatly reducing, the pitting of a plurality of glass sheets disposed in superimposed contacting relationship during the simultaneous heating and bending thereof.

A further object of the invention is to provide a method and apparatus for retarding the heating of the unsupported corresponding edges of a plurality of superimposed glass sheets during the initial heating period of a bending operation.

A still further object of the invention is to provide a novel bending mold including a flexible, interwoven meshed screen or curtain which is carried by the mold in a manner to project downwardly over and in contact with at least the unsupported edges of glass sheets positioned thereon when the sheets are in the relatively flat, unbent condition.

Other objects and advantages of the invention will become more apparent during the course of the following description when taken in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate like parts throughout the same:

FIG. 1 is a longitudinal, cross sectional view of a bending apparatus in accordance with the present invention, and shown in its open position;

FIG. 2 is a longitudinal, cross sectional view of the mold shown in FIG. 1 when in its closed position;

FIG. 3 is a front elevational view of the mold in accordance with the invention, when in its open position;

FIG. 4 is a partial transverse, cross sectional view taken along the line 44 of FIG. 1; and

FIG. 5 is a partial transverse, cross sectional view similar to FIG. 4 but illustrating a modified form of the invention.

Briefly stated, the present invention provides a method for preventing the marring or pitting of the contacting surfaces of a plurality of glass sheets disposed in superimposed relationship by the steps of retarding the heating of the unsupported edges of the sheets during the initial heating period of the bending operation, and simultaneously preventing the entry of foreign matter present in the bending furnace atmosphere into the space between the contacting surfaces of the sheets caused by the bowing thereof.

In addition, the apparatus according to the present invention comprises a bending mold including a shaping surface which defines the curvature of the marginal area of the sheets to be bent thereon and is adapted to support a plurality of unbent flat sheets in stacked superimposed relationship. The novel mold includes a support which extends above the shaping surface thereof, and particularly above the shaping surface portions which are not disposed in contact with the lowermost glass sheet when in the unbent condition. The support in turn carries a thin curtain or shield member, for example, of metal cloth or an imperforate sheet material which projects downwardly over and in contact with those portions of the glass sheet edges which are initially unsupported by the mold shaping surfaces. In this manner then, the shield member acts to both retard the heating of the unsupported edge portions of the sheets as well as to effectively prevent the entry of foreign matter in the furnace atmosphere into the gap between the sheets as caused by the bowing thereof.

Referring now more particularly to the drawings, there is shown in FIG. 1 an improved glass bending apparatus designated generally by the numeral 11. The bending apparatus 11, for purposes of illustrating the present in vention, may suitably comprise a substantially rectangular mold 12 of the concave, hinged type which is used to simultaneously bend a plurality of glass sheets 13 and 14 supported in superimposed stacked relationship thereon to the complex curvatures required by present-day automobile Windshields and aircraft canopies.

The bending apparatus 11 also includes a supporting rack indicated generally at 15 which is substantially rectangular in shape and comprises spaced, longitudinal side rails 16 rigidly connected to one another at their opposite ends by end rails 17. As a means of guiding the rack through the glass bending furnace, a pair of spaced guide rails 18 are secured to the underside of the side rails 16 and may be associated with the conveyor rolls used in most bending furnaces.

The mold 12 is carried by or supported on the rack 15 by uprights or posts 19 spaced slightly inwardly from each of the opposite ends of the side rails 16 and rigidly secured to the upper surfaces thereof. In this connection, braces 20 are also employed and fixed to both the uprights 19 and the side rails 16. The mold is of the general type commonly termed an outline or skeleton mold and comprises a movable center section 21 and opposite end sections 22 movably connected at their inner ends to the center section. Each of the end sections and the center section have a portion of a shaping surface 23 formed thereon which conforms in both elevation and outline to the desired curvature of the glass sheets to be bent thereon.

The mold end sections 22 are pivotally connected to the center section 21 by hinges 24 and the entire mold 12 is carried on the rack 15 by transverse rods 25 secured to the end sections 22 and swingably supported at their ends in links 26. The links 26 are also swingably connected at their upper ends to pins 27 that are fixed in the uprights or posts 19.

By means of the hinges 24 and rods 25, the end mold sections 22 are adapted to be moved from a closed position such as shown in FIG. 2 to an open position such as shown in FIG. 1. In this manner then, in the open position, the mold supports two or more fiat glass sheets 13 and 14 in a horizontal position prior to the bending thereof. As the mold and glass sheets are passed through the furnace, the sheets become softened upon reaching a temperature of about 1100 F. and tend to sag. At this time, the mold end sections swing up wardly and inwardly and thus assist in bending the sheets into conformity with the shaping surfaces on the central and end mold sections.

Now it will be appreciated that when the mold 12 is in the open position, the sheets 13 and 14 are supported only at their transverse ends by the shaping surface portions 28 of the end sections 22, there being no contact of the shaping surface portions of the center section 21 or the longitudinally disposed shaping surface portions of the end sections 22 with the longitudinal edges of the sheets. Accordingly, it has been found that these unsupported edges of the sheets 13 and 14 tend to bow away from each other during the initial heating period of the bending operation and thus leave a gap therebetween, such as indicated at 29 in FIG. 4. The presence of such a gap, of course, enables the entry of foreign matter, present in the bending furnace atmosphere, between the sheets and, most importantly, also enables the entry of small glass particles spalled off these unsupported edges of the sheets. This results in sub= stantial marring or pitting of the surfaces of the sheets which later in the bending operation come into contact with each other, for example, when the mold 12 assumes the closed position illustrated in FIG. 2 and the sheets sag into conformity with the shaping surface portions of the mold sections which then form substantial continuations of each other.

In accordance with the present invention, and in order to prevent the rn-arring or pitting of the nested glass sheets 13 and 14, a pair of support rods 30 are provided and extend longitudinally of the mold 12, one on either side thereof. The rods 30 are positioned above the longitudinal extending shaping surface portions of the center and end mold sections by means of struts 31. The struts 31 are secured at one end to the uprights or posts 19 and at their other end to generally U-shaped brackets 32 into which the ends of the rods 30 are inserted. Additional support is provided by the bars 33 which extend between and are fixed to the posts 19 and struts 31.

A thin, flexible curtain 34 which, for example, may be composed of interwoven glass fibers to provide a mesh size smaller than approximately 200, is aflixed to the rod and extends or hangs downwardly therefrom along substantially the entire length of the rod, i.e. between the inner facing surfaces of the brackets 32. The flexible curtain member 34 is of a height which enables it to project downwardly past the longitudinal edges of the glass sheets when such are disposed in their unbent condition on the open mold, i.e. when only the transverse edges of the sheets are supported on the shaping surface. In addition, and as is best shown in FIG. 4, the struts 31 preferably extend inwardly to a point such that the rods 30 mounted in the brackets 32 are disposed slightly inwardly of the longitudinal edges of the sheets as carried by the mold 12, i.e. are within the projected periphery of the shaping surfaces or at least the projected periphery of the glass sheet edges. This positioning of the rods 30 assures that the flexible curtain 34 will hang in contact with the longitudinal edges of the sheets prior to movement of the mold sections into the closed position, such as shown in FIG. 2. Thus, the curtain 34 effectively blocks off and prevents entry of foreign matter into the gap 29 produced by the bowing of the sheets 13 and 14 when same are initially heated and the mold 12 is in the open position.

Now it will be appreciated that although the curtain 34 will prevent entry of dust particles or the like from the atmosphere into the gap 29, it does not physically prevent small particles of glass spalled ofi from the outermost, opposed inner surfaces of the longitudinal sheet edges from entering into the gap. However, it has been found that the provision of the curtain 34 in some manner effectively prevents this edge spalling, at least to any substantial or harmful degree, and it is believed that such is due to the much greater surface area presented by the curtain 34 than by the sheet edges. In any respect, spalling, which to a great extent is caused by the initial rapid heating of the sheet edges, is substantially inhibited and the pitting problem, to any significant extent, eliminated.

While the employment of a flexible, interwoven meshed material or screen as the curtain 34 has been found to provide particularly excellent results and is preferable from the aspect of ease of mounting of the glass sheets on the mold, it will be appreciated that it is also possible to employ thin imperforate sheets of metal or other material, which may be rigid or semi-rigid, as the heat retarding and gap covering member. In this connection, such a construction is shown in FIG. 5, Wherein an imperforate thin metal sheet 35 is afiixed to the support rod 3t) and projects downwardly therefrom over and in contact with the edges of the glass sheets 13 and 14. In this embodiment, however, it is preferred that the support rods 30 be positioned so that the hanging portion of the sheet 35 forming the curtain lies substantially entirely in essentially the same vertical plane as the edges of the glass sheets. This is necessary in the case of a rigid material to assure that the sheet 35 is contiguous with the edges of all of the superimposed glass sheets.

In operation, and in accordance with the method of the invention, the mold 12 is first swung to the open position of FIG. 1 and a plurality of glass sheets, for example, the pair indicated at 13 and 14, are placed in superimposed stacked relationship thereon so that the transverse edges of the sheets are directly supported on the shaping surface portions 28 of the end sections 22, with the lowermost sheet 14 actually contacting these portions. In this manner then, the sheets act as strut members to hold the mold in the open position. The rods 30, together with the curtains 34 afiixed thereto, are then inserted into the brackets 32 so that the curtains hang downwardly over and in contact with the unsupported longitudinal edges of the sheets. The mold is then ready to be passed through a conventional bending furnace.

Upon entry of the mold 12 and supported glass sheets 13 and 14 into the furnace, the sheets are exposed to radiant heat and in many instances, particularly where rather severe bends are required in certain portions thereof, to direct flames from gas burners suitably positioned in the furnace. Due to the shield members or curtains 34, however, the heating of the unsupported edges of the sheets at their outrnost portions is retarded. At the same time, of course, the curtains 34 being in contact with the unsupported edges effectively prevent the entry of dust particles and the like in the furnace atmosphere from being blown into the gap or opening 29 produced between these edges, -due to the bowing of the sheets during this initial heating period. The curtains remain in contact with the longitudinal edges until the sheets become softened to the point where they tend to sag. At this time, the strut characteristic of the sheets i destroyed and the mold sections begin their movement into the closed position of FIG. 2. Also, at this time, the bowing of the sheets, or more particularly the upper sheet, ceases whereby the gap 29 closes and the sheets become nested. In this manner then, by the time that the unsupported edges of the sheets become disposed beneath the bottom edges of the curtains 34, the ga 29 has disappeared and the danger of entry of foreign matter between the sheets has passed.

While the employment of either an interwoven flexible material or a rigid or semi-rigid material as the curtain 34 has been found to effectively retard the heating of the unsupported edges of the sheets, it is also possible to coat the edges and outermost marginal areas of the sheets with a heat-reflective paint or slurry. Thi would serve, in a similar manner, to substantially retard the rapid heating of the unsupported edges and thereby revent the spalling of glass from these edges. However, in using this method, extreme care must be taken in eliminating substantially all severe currents in the bending furnace which would tend to blow dust particles and the like into the gap 29 between the sheets. In this same connection, it would, of course, also be possible to employ a curtain such as shown at 34 together with a coating applied to the sheet edges whereby the curtain could be spaced somewhat from the unsupported sheet edges and need perform only the function of screening the foreign material from entry into the gap.

It is to be understood that the forms of the invention herewith shown and described are to be taken as illustrative embodiments only of the same, and that various changes in the shape, size and arrangement of parts, as well as various procedural changes may be resorted to without departing from the spirit of the invention.

I claim:

1. In a method of simultaneously bending a plurality of glass sheets disposed in superimposed stacked relationship upon a bending mold, wherein certain of the edges of said sheets are unsupported during the initial heating of the unbent sheets which permits such edges to separate and leave a gap therebetween, the steps of passing said mold and sheets supported thereon through a bending furnace, and retarding the heating of said unsupported edges during the initial heating period of the bending operation whereby the spalling of glass from said unsupported edges and entry thereof into said gap between the sheets is substantially eliminated.

2. In a method of simultaneously bending a plurality of glass sheets disposed in superimposed stacked relationship upon a bending mold, wherein certain of the edges of said sheets are unsupported during the initial heating of the unbent sheets which permits such edges to separate and leave a gap therebetween, the steps of passing said mold and sheets supported thereon through a bending furnace, retarding the heating of said unsupported edges during the initial heating period of the bending operation, and simultaneously preventing the entry of foreign matter present in the bending furnace atmosphere into said gap between the sheets.

3. In a method of simultaneously bending a plurality of glass sheets disposed in superimposed stacked relationship upon a bending mold, wherein certain of the edges of said sheets are unsupported during the initial heating of the unbent sheets which permit such edges to separate and leave a gap therebetween, the steps of passing said mold and sheets supported thereon through a bending furnace, absorbing heat from the furnace immediately adjacent said unsupported edges during the initial heating period of the bending operation to retard the heating thereof, and simultaneously preventing the entry of foreign matter present in the bending furnace atmosphere into said gap between the sheets by covering said gap with a curtain disposed over and in contact with said unsupported edges.

4. In an apparatus for simultaneously bending a plurality of superimposed stacked glass sheets, a rack, a mold carried by said rack, said mold including a shaping surface conforming in curvature to that of the sheets when bent and adapted to receive said sheets and support a portion of the edges thereof when the sheets are in a fiat unbent condition, a support carried by said rack so as to extend above said shaping surface, and a thin curtain of heat absorbing material fixed to said support, said curtain projecting downwardly from said support over and in contact with those portions of the glass sheet edges which are unsupported by said shaping surface when said sheets are in said unbent condition.

5. In an apparatus for simultaneously bending a plurality of superimposed stacked glass sheets, a rack, a mold carried by said rack, said mold including a shaping surface conforming in curvature to that of the sheets when bent and adapted to receive said sheets and support a portion of the edges thereof when the sheets are in a fiat unbent condition, a support carried by said rack so as to extend above said shaping surface, and a thin, small mesh, flexible screen of heat absorbing material fixed to said support, said screen projecting downwardly from said support over and in contact with those portions of the glass sheet edges which are unsupported by said shaping surface when said sheets are in said unbent condition.

6. In an apparatus for simultaneously bending a plurality of superimposed stacked glass sheets, a sectionalized bending mold comprising -a plurality of mold sections each having shaping surfaces formed thereon, means mounting said mold sections for movement between an open position wherein said shaping surfaces are adapted to support only portions of the edges of the superimposed fiat glass sheets to be bent and a closed position in which said shaping surfaces form substantial continuations of each other and define the curvature to which the fiat sheets are to be bent, a plurality of. supports, means mounting said supports above said shaping surfaces of said mold sections, and a thin, small mesh, flexible screen of heat absorbing material fixed to each said support, said screens extending downwardly from said supports over and in contact with those portions of the glass sheet edges which are unsupported by said shaping surfaces when said mold is in the open position but out of contact with substantially all such edge portions when said mold is in said closed position.

7. An apparatus in accordance with claim 5, in which said supports are positioned substantially horizontally above said shaping surfaces and within the projected periphery thereof.

References Cited by the Examiner UNITED STATES PATENTS 782,967 2/1905 Kinon 6524 2,608,030 8/1952 Jendrisak 65287 2,872,755 2/1959 Lawson 65-287 3,069,878 12/1962 Carson et al. 65l07 DONALL H. SYLVESTER, Primary Examiner. 

1. IN A METHOD OF SIMULTANEOUSLY BENDING A PLURALITY OF GLASS SHEETS DISPOSED IN SUPERIMPOSED STACKED RELATIONSHIP UPON A BENDING MOLD, WHEREIN CERTAIN OF THE EDGES OF SAID SHEETS ARE UNSUPPORTED DURING THE INITIAL HEATING OF THE UNBENT SHEETS WHICH PERMITS SUCH EDGES TO SEPARATE AND LEAVE A GAP THEREBETWEEN, THE STEPS OF PASSING SAID MOLD AND SHEETS SUPPORTED THEREON THROUGH A BENDING FURNACE, AND RETARDING THE HEATING OF SAID UNSUPPORTED EDGES DURING THE INITIAL HEATING PERIOD OF THE BENDING OPERATION WHEREBY THE SPALLING OF GLASS FROM SAID UNSUPPORTED EDGES AND ENTRY THEREOL INTO SAID GAP BETWEEN THE SHEETS IS SUBSTANTIALLY ELIMINATED.
 4. IN AN APPARATUS FOR SIMULTANEOUSLY BENDING A PLURALITY OF SUPERIMPOSED STACKED GLASS SHEETS, A RACK, A MOLD CARRIED BY SAID RACK, SAID MOLD INCLUDING A SHAPING SURFACE CONFORMING IN CURVATURE TO THAT OF THE SHEETS WHEN BENT AND ADAPTED TO RECEIVE SAID SHEETS AND SUPPORT A PORTION OF THE EDGES THEREOF WHEN THE SHEETS ARE IN A FLAT UNBENT CONDITION, A SUPPORT CARRIED BY SAID RACK SO AS TO EXTEND ABOVE SAID SHAPING SURFACE, AND A THIN CURTAIN OF HEAT ABSORBING MATERIAL FIXED TO SAID SUPPORT, SAID CURTAIN PROJECTING DOWNWARDLY FROM SAID SUPPORT OVER AND IN CONTACT WITH THOSE PORTIONS OF THE GLASS SHEET EDGES WHICH ARE UNSUPPORTED BY SAID SHAPING SURFACE WHEN SAID SHEETS ARE IN SAID UNBENT CONDITION. 